My nearside front door is rather erratic when it comes to central locking at the moment. Occasionally the pin will not pop up when I press the key (to unlock and disarm the alarm) and so the other door pins drop again. It also refuses to drop sometime and so the the other door pins drop and then pop up again. I have to turn the key in the problematical door and then press the key to lock all of the others. Could it be a sticking mechanism or something like that?